The present invention is particularly applicable to the production of sheet metal strands or strips from an elongated sheet metal web or strip, and will be described with reference thereto. However, it is understood that the invention has broader applications including the production of strips or strands of other types or gauges of metal materials initially produced in flat or wide strip form.
It is often desirable, as in the motor lamination industry, to produce great quantities of small oval or circular pieces of metal for the stator cores of electric motors. Such pieces are commonly produced by cutting a sheet or elongated strip of sheet metal into narrow individual strips or strands, and then punching or stamping out a closely spaced linear array of oval or circular pieces from each strand. In order to reduce waste material remaining after the pieces are stamped out of a sheet metal strand, it is necessary to space the pieces as closely as possible along the length of the strand. More importantly, and involving considerably greater difficulty, is the need to maintain the width of the sheet metal strand as closely as possible to the diameter of the desired end products. Minimizing the excess width of the strand reduces the waste material which necessarily is produced in the form of two thin, irregular strands representing the sides of the original strand extending between and laterally beyond the oval or circular portions.
It is known to address the problem of reducing waste material by cutting a master strip or web of sheet metal into individual strands or strips having non-linear edges. Non-linear edges which successively converge and diverge will define longitudinally successive portions of relatively greater width joined by successive portions of relatively lesser width. The portions of greater width provide the material for the finished end product pieces, which may be circular, oval, diamond shaped, or of any outline for which a closely spaced array of pieces is desired. When the non-linear edges are cut in curvilinear shape, the varying strand width will more closely match a linear array of ovals or circles to be stamped from within the strand and will thereby leave less unused strand material as waste. Mechanical gang slitting knives are commonly used to cut strips with diverging and converging strand edges from a moving web of metal sheet material in a time consuming and expensive process. Such knives have scalloped side faces and are extremely expensive and difficult to sharpen. Another disadvantage inherent in such knife cutting systems is the requirement for a different set of knives for each size and pattern of end product pieces, and hence strand edge patterns, desired by the user. Knife cutting systems further require complex mechanisms to maintain a necessary level of tension in the sheet material at and across the cutting surface. Lost production time during knife changeovers adds to the expense of these prior art systems.
It is also known that high energy beams can be used as a more efficient and effective means to cut sheets of material into strips. For example, cutting beams have been used in this manner to produce composite sheets of laminated material which are readily separable into strips of one or more individual layers. One such apparatus is disclosed in U.S. Pat. No. 4,537,809 to Ang et al., which disclosure is incorporated herein by reference and is exemplary of prior art energy beam cutting devices. The Ang et al. apparatus disclosed in this patent is useful in a process wherein the cut strands or strips themselves are the finished end product. The Ang et al. disclosure shows coextensively non-linear strand edges of corresponding in-phase curvature and does not address the need to control and vary the width of each strand in an opposed diverging and converging edge pattern to minimize waste produced when the end product is stamped out from within the strand. The prior art in the field of high energy beam cutting is thus seen to fail to overcome the above noted disadvantages inherent in knife cutting systems for producing strands with edge patterns as demanded by variously shaped sheet metal end products to be stamped therefrom.